In 1965, Gordon Moore proposed that the number of transistors in a dense integrated circuit would double every year, aka. “Moore's Law”. Moore's prediction proved accurate for a number of decades, however various technical challenges have impeded the semiconductor industry in maintaining the initial predicted rate of growth. Currently, the predicted rate of growth is a doubling in component density every 2.5 years. One limitation on sustaining the growth initially predicted by Moore is the challenge in removing heat from a central processing unit (CPU) generated during operation of the CPU. A modern CPU can generate in excess of 100 W of waste heat, wherein the limitations of state-of-the-art thermal management technology fall short of what is required to sustain the growth curve of Moore's Law, a situation that has been termed the “thermal brick wall” problem.
FIG. 6 (prior art) illustrates a heat exchanger 600 (aka “SANDIA COOLER”) configured to extract heat energy from an underlying structure, as disclosed in U.S. Pat. No. 8,988,881. Heat exchanger 600 comprises a heat sink impeller (HSI) 605, which is configured to spin above a baseplate 610. Heat is removed from a component (e.g., a CPU or GPU) thermally attached to the bottom of the baseplate 610. The interior of the baseplate 610, in the embodiment depicted in FIG. 6, comprises a vapor chamber 612 to uniformly transmit a concentrated heat load entering the bottom surface of the baseplate 610 to the upper surface of the baseplate 610. The heat then flows across a thin air bearing and into the HSI, where it is rejected to the ambient surroundings by transferring from the HSI fins into the radially outward air flow.
Rotation of the HSI 605 is provided by a motor 645 (e.g., a brushless motor) connected to the bladed rotor 605 by a spindle 620. As the HSI 605 rotates, the plurality of blades cause air to be drawn from the ambient surroundings of the HSI 605 into the central portion and then down along the central region of the spindle 620, where the air exits the HSI 605 radially through the blades. Lift of the HSI 605 from the baseplate 610 is created due to relative rotation of the stationary baseplate and the rotating HSI 605 (e.g., through use of a series of spiral-shaped grooves in the baseplate 610), wherein the air gap is a hydrodynamic air bearing. With continued operation of the HSI 605, the air gap is maintained, while heat travels across the air gap and is rejected to the ambient surroundings through the HSI 605 (i.e., into the air that flows radially through the blades).
The air bearing comprises a portion of the thermal circuit, and therefore it is important to ensure that it remains thin (on the order of 10 microns) to keep a low thermal resistance and avoid performance loss. In the conventional heat exchanger 600, for optimal performance, orientation of the heat exchanger 600 is limited to a single orientation, where the baseplate 610 is placed on top of a surface, and the HSI 605 is above the baseplate 610. This is because the weight of the HSI 605 (along with a spring 630 that provides a force that is less than the weight of the HSI 605) is used to maintain the thickness of the air gap (e.g., the weight of the HSI 605 prevents the air gap from becoming too large). If the orientation of the heat exchanger 600 were to be altered (e.g., such that the HSI 605 were below the baseplate 610), then the size of the air gap would be larger than desired.